Current-sensors are often utilized in circuits for high performance control of electric machine drive systems and fault detection. In the automotive industry, applications include electric power assist steering and various other auxiliary systems and electric, hybrid electric and fuel cell electric vehicles. One primary difficulty experienced by robust control using current-sensors is obtaining an accurate and reliable sensed signal. Fluctuations, caused by device tolerances, temperature, age and noise, in the gains of current-sensors and their related circuits can affect the efficiency and accuracy of the system.
Current-sensor gains include input to output gain of the actual current-sensor and current-sensor to analog-to-digital (A/D) interface circuit gains.
Presently, precision compensation for current-sensor gain errors is accomplished through post-production manual calibration and tends to involve high cost precision devices and unreliable trim potentiometers. To maintain accuracy, these difficult manual calibrations are repeated at various times over the life of the system, or the gains used in software are periodically adjusted. Manual calibration cannot, however, substantially compensate for variations due to temperature effects and noise during operation of the system. Additionally, in a high volume production scenario, manual calibration is costly and time consuming, and it tends to make each system undesirably unique.
The disadvantages associated with current methods for compensating for current-sensor gain errors in electric machines have made it apparent that a new method to compensate for current-sensor gain errors is needed. The new technique should substantially reduce manual calibrations and should require relatively inexpensive components with low tolerance specifications. The new technique should also maintain a high level of accuracy and robustness. The present invention is directed to these ends.